Equivalent high-power pulsed microwave transmitter



Feb. 19, 1963 CARTER AL 3,078,424

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INVENTORS, JOHN L. CARTER BY IRVING RE] OLD.

A T TORNE X United States Patent Ofilice 3,078,424 iatented Feb. 1%,1953 3,073,424 EQUEVALENT HiGH-FtlWEi'it PULSE Miit- WAVE TRANSMHTTERiohn L. Carter, Asbury Park, and lirving Reiugold, Deal Paris, Deal, Ni,assignors to the United States of America as represented by theSecretary of the Army Fiied duly 3, 1961, Ser. No. 121,789 5 Claims.(Ci. 333 (Granted under Title 35, US. Code (1%2), sec. 2.66)

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment of anyroyalty thereon.

This invention relates to microwave pulse transmission systems and moreparticularly to a pulsed transmission system utilizing a travelling-wavering resonator.

The utilization of a reentrant closed waveguide travelling-wave ringresonator loop as microwave power multipliers has been known for sometime. While such multipliers havc heretofore been adapted only fortesting microwave components at high power while using a low powermicrowave source, the advantages of utilizing the multiplied power as atransmitted pulse has long been recognized in the art. It is thereforean object of the present invention to provide a pulse transmissionsystem utilizing a microwave power multiplier of the travelling-waveresonator closed loop type which is driven by a relatively low microwavesource.

In accordance with the present invention the pulsed microwave circuitincludes a source of relatively low incident power which is coupled to areentrant closed loop waveguide such that the incident power ismultiplied within the loop. The reentrant closed loop waveguide includesan evacuated waveguide structure filled with an ionizable gas and havinga longitudinal waveguide branch and a waveguide branch orthogonallypositioned thereto. Discrete multipactor type switches are mountedacross each of the waveguide branches and respectively spaced a distanceof one-half wavelength of the operating frequency from the junction ofthe longitudinally and orthogonally positioned waveguide branches. Alsoincluded are means for simultaneously activating the multipactorswitches such that the incident power is multiplied in the closedwaveguide loop when the multipactor switch in the longitudinalwaveguidebranch is energized and the switch in the orthogonal waveguidebranch is deencrgized, and the multiplied power is derived from theorthogonal waveguide branch when its associated multipactor switch isenergized and the switch in the longitudinal waveguide branch isdeenergized. The conditions for the energized and deenergized states ofthe multipactor switches are set forth hereinbe'low.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the single FIGURE of the accompanying drawing.

Referring now to the figure in the drawing, there is shown at in adirectional coupler having high directivity and including two sectionsof hollow rectangular waveguides 12 and 14 having a directional couplingaperture 15 in the common Wall between the sections of waveguides 12 and14. The waveguide section 12 is connected at one end through rectilinearwaveguide 18 to a microwave input source indicated schematically at 20.the other end of waveguide section 12 being terminated by anon-reflective load 22. Opposite ends of waveguide section 1.4 areconnected by respective waveguide loop sections 24 and 26 to anevacuated waveguide section 28, herein shown as comprising twoorthogonally related rectangular waveguide branches 3% and 32 having acommon waveguide junction as at 34 and arranged such that the transversedimension of waveguide 32 is coextensive with the longitudinal dimensionof waveguide branch 30. The waveguide branches 3t) and 32 are sealed bylarge lowloss non-resonant glass Windows as shown at 36, 38 and id toprovide a vacuum tight seal and the entire sealed area is provided withan ionizable gas such as argon at a pressure in the region of l0 mm. ofHg. Waveguide loop sections 24 and 26 are terminated by the sealed endsof horizontally disposed waveguide branch 30. As shown, within theorthogonally positioned waveguide branches Ed and 32 there are providedrespective high vacuum switches 42 and 44 whose operation depends on anelectron multiplying process usually referred to as a multipactordischarge and will hereinafter be referred to as multipactor typeswitches. Each switch includes a pair of spaced, oppositely arranged,truncated cone shaped electrodes whose opposing ends are coated with ahigh secondary emission material such as manganese or beryllium copper.The spaced truncated cone electrodes of switch 42 disposed withinhorizontal waveguide branch 30 are shown at as and 4-8 and the spacedtruncated cone electrodes of switch 44 disposed in waveguide branch 32.are shown at St and 52. Truncated cone electrodes 43 and 52 areelectrically isolated from their respective waveguide branches bysuitable vacuum tight dielectric seals as at 54, 5d and, as shown,respective positive D-C. bias sources 58 and 6d are connected acrosseach of the high vacuum switches 42 and 4d. Each bias source may have avalue of several hundred volts and each is provided with an on-ofiswitch which may be gauged to provide alternate on-off switching of therespective D.-C. bias sources. Multipactor switches 42 and 44 arearranged such that their respective centers are spaced one-halfwavelength at the operating frequency from waveguide junction 34. Theresonant type multipactor build-up normally provided by the multipactorswi ches hereinabove described are prevented by the application of theD.-C. biases. The application of the postive D.-C. bias creates anelectric field which sweeps electrons out of the ionized region, thushindering the ionization process. Thus, with the D.-C. 'ias from sourceso applied to multipactor switch 44, the switch transmits the incidentpower with very little insertion loss. However, with no D.-C. biasapplied to multipactor switch 44, an electron discharge is built upacross the electrodes thereof due to the ionization of the gas withinthe evacuated waveguide section 9.8 so that a short circuit appears atwaveguide junction 34 to effectively provide a continuous waveguidecircuit along the longitudinal dimension of waveguide branch 38.Similarly, with no D-C. bias applied to multipactor switch 42, aneffective short circuit will appear across the transverse dimension ofwaveguide branch 30 at junction 34 due to the electron discharge builtup across the elec trodes of switch 42. With D.-C. bias applied toswitch 42, it transmits the incident power from source 2% with verylittle insertion loss as hereinafter explained. For purposes of thisapplication, with no D.-C. bias applied, the multipactor switches willbe designated as being in the energized or discharge condition, and,with D.-C. bias applied, the multipactor switches will be designated asbeing in the deenergized or non-discharge condition. With muitipactorswitch 44, hereinafter referred to as the output multipactor switch, inthe electron discharge condition and with multipactor switch 42 in thenondischarge condition, a, reentrant or closed loop waveguide sectioncommonly known in the art as a travelling-wave ring resonator is formedby the open ended terminations of waveguide section 14 of directionalcoupler 10, waveguide loop sections 24 and 26 and sealed-01f branch 36.The electrical length of the travelling-wave ring resonator loop is madean integral number of guide wavelengths of the operating frequency.

aovsnsa The operation of the travelling-wave ring resonator as a powermultiplier is well known in the prior art and is described in SferrazzaPatent No. 2,875,415, issued February 24, 1959. The power multiplicationof such a ring resonator may be briefly described as follows. Assume anincident wave from the source 25, travelling along tr e waveguidesection 12. A portion of this energy is coupled into the waveguidesection 14 as a coupled wave, and a portion continues down waveguide 12as a direct wave to the load 22;. The coupled wave travels around theloop formed by loop sections 24 and 26 and evacuated waveguide section30 which includes multipact-or switch 42. At the coupling aperture 16again this energy is divided, 2. portion being coupled to the load 22and a portion recirculating around the closed loop. If the phase of theportion recirculating around the closed loop is such as to add to thecoupled wave from the source 20, the energy in the closed loop will belarger than during the first passage around the loop. This build-up ofenergy will continue with each cycle around the loop until the losseswithin the loop and absorption of energy by the load 22 exactly balancethe output of the source 29-. Assuming the attenuation around the loopis zero, a steady state condition will be reached when the energycoupled to the load 22 is exactly equal to the energy output of source20. There will be partial cancellation at the load 2 of the energycoupled from the loop to the rectilinear guide 18 and the incidentenergy from source 20 passing through to load 22. Hence, the energylevel in the loop during the steady state is at a higher level than theenergy level at load 22. Under such circumstances, the smaller theamount of coupling, the greater is the energy stored in the form of atravelling-wave around the closed loop, and the more cycles of the wavein the closed loop before the steady state condition is reached. This isso because of the relatively small increment of energy that is coupledout of the closed loop for each cycle. If the loop is made manywavelengths long, power magnification of and times may be achieved.

The power multiplication of course continues so long as no D.- C. biasis applied to output multipactor switch 44 and D.-C. bias is applied tomultipactor switch 42. When the steady state condition within the loopis reached, the D.-C. bias is applied to output multipactor switch 44and, simultaneously, the D.-C. bias is removed from multipactor switch42 by any suitable means. During this condition, the power within theloop is passed through evacuated waveguide branch 32 to a utilizationcircuit such as an antenna, for example. The duration of the outputpulses is made to be the same as the duration of the transit time of theWavefront around the closed loop. The nature of the multipactor switchis such that the recovery time will be less than 0.01 microsecond. Theoutput switch 44- is placed on the loop so that in emptying the ring ofpower, only a minimum part of the energy passes the directional couplerit).

While there has been described what is at Present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A pulsed microwave circuit comprising a source of relatively lowincident power, a reentrant closed loop waveguide ring resonator coupledand responsive to said incident power whereby said incident power ismultiplied within said loop, said reentrant closed loop waveguide ringresonator including an evacuated waveguide structure filled with anionizable gas and having a longitudinal waveguide branch and a waveguidebranch orthogonally positioned thereto, discrete multipactor typeswitches mounted across each of said branches, and means forsimultaneously activating said switches such that the incident power ismultiplied in said loop when the multipactor switch in the longitudinalwaveguide branch is energized and the switch in said orthogonalwaveguide is deenergized, and said multiplied power is derived from saidorthogonal waveguide branch when its associated multipactor switch isenergized and the switch in said longitudinal waveguide branch isdeenergized.

2. A pulsed microwave circuit comprising a source of relatively lowpower incident wave energy, a reentrant closed loop waveguide ringresonator including an evacuated waveguide structure comprising a firstlongitudinal waveguide branch and a second waveguide branch orthogonallypositioned relative to said longitudinal waveguide branch, saidwaveguide branches being arranged such that the transverse dimension ofsaid orthogonally positioned waveguide is coextensive with thelongitudinal dimension of the other waveguide branch, said evacuatedwaveguide structure including an ionizable gas, means forming a part ofsaid loop for coupling said incident wave energy into said closed loop,discrete multipactor switch means positioned across said orthogonal andlongitudinal waveguide branches whereby the incident signal power ismultiplied in said loop when the switch means in said longitudinalwaveguide branch is energized, and the switch means in said orthogonalwaveguide branch is deenergized, and the multiplied power signal isderived from said orthogonal waveguide when the switch means in saidlongitudinal waveguide branch is deenergizcd, and the switch means insaid orthogonal waveguide branch is energized.

3. A pulsed microwave circuit comprising a rectilinear input waveguideterminated atone end by energy absorbing means and a source of incidentelectromagnetic wave energy coupled to the other end of said inputwaveguide, an evacuated sealed waveguide structure filled with anionizable gas and including a first longitudinal waveguide branch and asecond Waveguide branch orthogonally positioned relative to saidlongitudinal waveguide branch, and having a common waveguide junction,said waveguide branches being arranged such that the transversedimension of said orthogonally positioned waveguide is coextensive withthe longitudinal dimension of the other waveguide branch, at first andsecond multipactor type discharge switch respectively mounted acrosssaid longitudinal and said orthogonal waveguide branches at respectivedistances one-half wavelength from said common unction, said switchesbeing insulated from respective waveguides in which they are mounted, adirectional couple r having four waveguide terminals, two of saidwaveguide terminals being in coupling relationship with said rectilinearwaveguide intermediate said source and said energy absorbing means, afirst waveguide section interconnecting the third waveguide terminal ofsaid directional coupler and one end of said longitudinal waveguidebranch, a second waveguide section interconnecting the fourth waveguideterminal of said directional coupler and the other end of saidlongitudinal waveguide branch, discrete biasing voltages respectively incircuit with said multipactor type switches for alternately renderingsaid switches On and Oil, such that when a bias voltage is applied tothe first multipactor switch, the third and fourth directional couplerwaveguide terminals, said first and second waveguide sections and saidevacuated longitudinal waveguide branch form a closed loop to multiplythe incident input power, and when a bias voltage is applied to saidsecond multipactor type switch, multiplied power energy is derivedthrough said orthogonal waveguide branch.

4. The pulsed microwave circuit in accordance with claim 1, wherein eachor" said multipactor switches comprise two opposing truncated coneshaped electrodes with opposing ends coated with a high secondaryemission material, the base of each of said truncated cone shapedelectrodes being insulated from its respective associated waveguide.

5. A pulsed microwave circuit comprising a source of relatively lowincident power, a reentrant closed loop waveguide ring resonator coupledand responsive to said incident power, said reentrant closed loopwaveguide ring resonator including an evacuated waveguide structurefilled with an ionizabie gas and having a first waveguide branch as anintegral portion of said loop and a second waveguide branch having acommon junction with said first waveguide branch within said loop butangularly positioned with respect to said first waveguide branch,discrete multipactor type switches mounted across each of said waveguidebranches, and means for activating said switches such that the incidentpower is multiplied in said loop when the multipactor switch in saidfirst waveguide branch is energized and the switch in said secondwaveguide branch is deenergized, and said multiplied power is derivedfrom said second waveguide branch when its associated multipactor switchis energized and the switch in said first waveguide branch isdeenergized.

References Cited in the file of this patent UNITED STATES PATENTS2,875,415 Sferrazza Feb. 24, 1959 2,930,004 Coale Mar. 22, 1960

1. A PULSED MICROWAVE CIRCUIT COMPRISING A SOURCE OF RELATIVELY LOWINCIDENT POWER, A REENTRANT CLOSED LOOP WAVEGUIDE RING RESONATOR COUPLEDAND RESPONSIVE TO SAID INCIDENT POWER WHEREBY SAID INCIDENT POWER ISMULTIPLIED WITHIN SAID LOOP, SAID REENTRANT CLOSED LOOP WAVEGUIDE RINGRESONATOR INCLUDING AN EVACUATED WAVEGUIDE STRUCTURE FILLED WITH ANIONIZABLE GAS AND HAVING A LONGITUDINAL WAVEGUIDE BRANCH AND A WAVEGUIDEBRANCH ORTHOGONALLY POSITIONED THERETO, DISCRETE MULTIPACTOR TYPESWITCHES MOUNTED ACROSS EACH OF SAID BRANCHES, AND MEANS FOR